1. Field of the Invention
The invention relates to a drive device that includes a vibration actuator. The drive device is capable of transporting linear, sheet or fiber like elements. The drive device can run by itself and be used as a "self-propelled device". A drive device, which is equipped with a vibration actuator, comprises an ultrasonic motor, and exhibits good controllability, a high durability and a quiet operation.
2. Description of the Related Art
Known vibration actuators can be divided into two main groups, a rotation actuator group and a linear actuator group. A rotation actuator can be used, for example, as a motor for a camera autofocus device.
FIG. 11 shows a drawing of a known linear vibration actuator. The linear vibration actuator includes a transformer 102, located at one end of a rod-shaped elastic member 101, to vibrate the elastic member 101. A second transformer 103 for controlling the vibrations is located at the other end of the rod-shaped elastic member 101. Vibration elements 102a and 103a are connected to transformers 102 and 103. An alternating voltage can be applied to the vibration element 102a to cause a vibration from the generator 102b to be transferred to the rod-shaped elastic member 101. The vibration is transformed into a travelling wave throughout the rod-shaped elastic member 101. An element to be moved 104 is placed on the rod-shaped elastic member 101, and moved by the travelling waves.
The vibration in the rod-shaped elastic member 101 is transmitted from the vibration element 103a through the transformer 103. The transformer 103 can control the vibration energy. The vibration energy is converted to electrical energy by the vibration element 103a. The electric energy is then consumed or absorbed by a load 103b that is connected to the vibration element 103a. Thus, a reflection of the wave at the edge surface of the rod-shaped elastic member 101 is controlled by the transformer 103 and the creation of standing waves in an intrinsic mode in the rod-shaped elastic member 101 is prevented.
The linear vibration actuator shown in FIG. 11 should have a length equal to that of the rod-shaped elastic member 101. Furthermore, it may be necessary to add vibrations to the rod-shaped elastic member 101 to move the element 104. Thus, a problem exists in that a transformer 103 is required for controlling vibrations, in addition to enlarging the device and preventing the creation of the standing waves.
In order to solve the above-noted problems, various types of vibration actuators have been proposed. For example, FIGS. 12(A)-12(C) are drawings showing a known longitudinal L1-bending B4 mode flat-plate motor 1', which can serve as an optic movement pick up. FIG. 12(A) is a front view, FIG. 12(B) is a side view and FIG. 12(C) is a planar view of the motor 1'.
The motor 1' includes an elastic member 1 comprising a rectangular flat plate shaped base part 1a and projected parts 1b and 1c, which are formed on one surface of the base part 1a. Piezoelectric members 2 and 3 comprise electro-mechanical converting elements and are attached to the other surface of the base part 1a of the elastic member 1. The electro-mechanical converting elements 2 and 3 create the longitudinal vibration and the bending vibrations on the surface of the elastic member 1.
The projected parts 1b and 1c are located at an antinode position of the bending vibration, that is generated in the base part 1a. The projected parts 1b and 1c contact an element to be moved (not shown), such as, for example, a guide rail and the like.
Further, a vibration actuator using a double mode bending vibration element has been known for use as a card transfer or paper feeding devices. See "New Version of Ultrasonic Motor," by Ueha and Tomikawa, published by Trikeps, pp. 161-165. With a card transfer or paper feeding device, a roller is rotated using an ultrasonic or vibration actuator. Cards or paper that contact the roller are moved by the actuator. However, if a round rod-shaped linear element is attempted to be moved by the vibration actuator of FIG. 12, problems arise.
FIGS. 13(A) and 13(B) illustrate the some of the above-noted problems. FIGS. 13(A) and 13(B) are drawings showing a roller element of a known driving device, using the vibration actuator of FIG. 12. In the driving device, a lower section of a roller 6 contacts the elastic member 1 and an element 4 to be moved, for example either a linear or sheet element. However, if a coefficient of friction for the surface of the roller 6 contacting the elastic member 1 differs from the coefficient of friction for the surface of the roller 6 contacting the element 4, efficient driving of the linear element 4 is not possible.
Additionally, if foreign matter adheres on the linear element 4, the foreign matter may enter the space between the roller 6 and the elastic member 1. Thus, the surface of the roller 6 has an increased friction, which reduces the durability of the lower section of the roller 6. Further, the driving efficiency is reduced and, in a worse case scenario, the roller 6 may not be able to be rotate. Additionally, the drive surface may be damaged by the foreign matter.
Where the element 4 is linear and driven by cylindrical rollers 5 and 6, the linear element 4 may slip sideways toward the advancing direction and against a lower section of the roller 6. Furthermore, in a worst case scenario, the linear element 4 may be become derailed from the lower section of the roller 6.